Obviously we hit a grey area with this situation. I personally do not agree with six and think the defenition of DOS needs to be defined in respect to youtube and it's users videos. I remember hearing something that we (as students) are not allowed to upload our work to youtube because it voids our ability to enter contests as youtube claims ownership over it. Vimeo is the only allowed site to upload.
Since youtube removes the reported videos that may be there own it might not be a DOS attack.